This invention relates to power converters, and, more particularly, to power converters with synchronous rectifier output stages.
Alternating current (AC) power is typically supplied from wall outlets and is sometimes referred to as line power. Electronic devices often include circuitry that runs from direct current (DC) power. AC to DC power converter circuitry can be used to convert AC power to DC power. The DC power that is created in this way may be used to power an electronic device that runs on DC power. The DC power that is created may also be used to charge a battery in an electronic device.
AC to DC power converters often include transformers. A transformer in an AC to DC power converter may have primary and secondary windings. A pulse width modulation (PWM) circuit on the primary side of a transformer may generate pulses of current that pass through the primary winding of the transformer. On the secondary side of the transformer, a diode may be used to rectify the output of the secondary winding.
Some AC to DC power converter circuits use synchronous rectifier (SR) output stages. SR output stages include a metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET is driven so as to rectify the output waveform from the transformer in the same way that the diode is used in other power converter designs while avoiding high diode voltage drops when conducting current.
The use of SR output stages may improve efficiency at high loads, but can lead to undesired switching losses at lower loads. It would therefore be desirable to be able to improve power converter circuits such as power converter circuits with SR output stages.